We propose to investigate the sites and mechanisms of action of FSH and androgens on cells of the seminiferous tubule, with focus on the control of metabolic and structural responses of Sertoli cells in culture. Responses to be evaluated include cyclic AMP formation; the production and secretion and androgen binding protein, inositol, and plasminogen activator; and the synthesis of other proteins. Factors regulating Sertoli cell structure and functions at different stages of development will be determined. We shall concomitantly investigate the nature of cell-cell interactions in the testis, with emphasis on the interrelations between Sertoli cells and germinal cells, and the mechanisms by which Sertoli cells influence spermatogenesis. We shall evaluate the hypothesis that control of spermatogenesis by FSH and androgens is mediated by direct actions on Sertoli cells, which then influence germinal cell development by creating a unique microenvironment within the seminiferous tubule.